The cooling cycle of a refrigeration system has been enhanced by diverting a portion of the main refrigerant stream flowing to an evaporator, expanding the diverted portion, and using the expanded refrigerant to cool the main refrigerant flow in a heat exchanger, which will be referred to as an economizer heat exchanger. The expanded refrigerant is returned to the compressor. It is an object of the present invention to utilize the economizer heat exchanger to enhance heating and/or defrost cycles, as well as the cooling cycle.